Examining the Effects of Irradiation Temperature on Defect Generation and the Nature of Dislocation Loops

TL;DR

This study investigates how different irradiation temperatures affect defect formation and dislocation loops in Grade 304L stainless steel, using proton irradiation, microscopy, and nano-indentation to understand microstructural and mechanical changes.

Contribution

It provides new insights into temperature-dependent defect evolution and segregation effects in stainless steel under irradiation, relevant for CANDU reactor components.

Findings

Defect types and densities vary significantly with temperature.

Interstitial dislocation loops are highly temperature dependent.

Radiation-induced segregation influences defect formation.

Abstract

Unlike the vast amount of irradiated material data that exists for stainless steel internals from LWRs, with high fast neutron flux and an irradiation temperature of~330oC, the CANDU reactor is unique with a high thermal spectrum stainless steel components peripheral to the core. In particular, the CANDU design contains an austenitic stainless steel calandria vessel, which contains the heavy water moderator at a temperature of 60-80oC. This article explores the effects of low (60-80oC) and moderate (300-360oC) irradiation temperature on irradiation induced defects and defect sinks, both in terms of microstructure and mechanical properties of Grade 304L stainless steel, irradiated with 3 MeV protons. State-of-the-art microscopy has been applied to characterize the irradiation defects, and nano-indentation performed to provide a link with the mechanical properties. It is hypothesized that the interstitial type of loops that develop is highly temperature dependent, and the formation of the defect loops is strongly linked with the amount of radiation induced segregation.